1. Technical Field
The present invention relates to an overload protector for a mechanical press.
2. Description of the Prior Art
There is a conventional device which is recited in Japanese Patent Publication No. 5-20629 the present inventor proposed earlier, as an example of the overload protector of this type.
The conventional device comprises an overload absorbing hydraulic chamber formed within a slide of a mechanical press and an overload protecting valve connected to this overload absorbing hydraulic chamber. The overload protecting valve has an interior area provided with a relief member and a valve closing spring of a pressure compensating valve. The relief member is adapted to act for valve closing through an urging force of the valve closing spring.
The above-mentioned pressure compensating valve serves to relieve pressurized oil within the hydraulic chamber by an amount corresponding to pressure increase when the pressurized oil has increased its pressure at a very slow speed from a set charging pressure during the press working. Therefore, it is necessary to set a relief pressure (hereafter referred to as `set compensating pressure`) of the pressure compensating valve at a value a little higher than the set charging pressure.
Consequently, in the case of enhancing the set charging pressure depending on the capacity and usage of the mechanical press, the set compensating pressure had to be increased accordingly. Similarly, in the case of decreasing the set charging pressure, the set compensating pressure had to be reduced.
The conventional technique is excellent in that it houses the pressure compensating valve within the overload protecting valve and therefore can be made compact. However, when changing the set compensating pressure, it was required to vary the urging force of the valve closing spring arranged within the overload protecting valve. This entailed a disadvantage that it took quite a labor to vary the urging force of the valve closing spring and effect a confirmation test after having varied it.